A controller area network (CAN) communication system is an in-vehicle network system for providing digital serial communication between various measurement and control apparatuses in a car. The CAN system reduces the weight and complexity by replacing complex electric wirings and relays of electric components in the car with efficient serial communication lines. The CAN system was developed using a network protocol for cars in 1980. Its protocol has excellent real-time control performance, is easy-to-implement, and widely used in the manufacturing industry, aviation, railways, and vehicles. CAN is established as a standard ISO 11898 by the International Organization for Standardization (ISO).
A typical structure of a CAN message includes a 1-bit start of frame (SOF) field, a 12-bit arbitration field, a 6-bit control field, a maximum 64-bit data field, a 16-bit cyclic redundancy check (CRC) field, a 2-bit acknowledge (ACK) field, a 7-bit end of frame (EOF) field, and a 3-bit inter frame space as illustrated in FIG. 1. The number of bits in each field is assigned according to the standard. Bits specified by 0 and 1 in a frame of the CAN message of FIG. 1 are transmitted on the CAN bus with a value specified in the standard. The standard allows for using a total 29-bit identifier by adding 18 bits to the 11-bit arbitration field.
The SOF field is transmitted first to indicate the start of the frame. The arbitration field following the SOF field includes either an 11-bit identifier or a 29-bit extended identifier and a remote transmission request (RTR) bit. The identifier field specifies a processing priority of the CAN message frame transmitted when communicating in the CAN. In order for the arbitration field to determine the priority, a unique identifier or identification number is assigned for each message of CAN data generated in each CAN controller. When the RTR bit has a value of “0” (default), it means that the CAN message contains data frame, and when the RTR bit has a value of “1,” it means that the CAN message contains remote frame. A remote frame is used when one node on a CAN bus requests data transmission from another node, and does not include a data field.
The control field is configured of 6 bits including 4 bits of data length code (DLC) which indicates the number of bytes of the data field and reserved bits R1 and R2 having a value of “0” to be used later.
The data field includes data to be transmitted from one node to another node with a maximum of 64 bits in length. The CRC field are used for checking cyclic redundancy and is made of 15 bit code and one delimiter bit having a value of “1” which indicates the end. The ACK field is composed of 2 bits. A receiver which has received a valid message correctly reports this to the transmitter by sending a value of “0” during the first slot bit. The second bit has a value of “1.”
The EOF field is configured of 7 bits all having values of “1.” The 3-bit inter frame space all having values of “1” follows the EOF field. After the 3-bit inter frame space, any node seeking to transmit may use the CAN bus. The node seeking to transmit may attempt to secure the bus by transmitting the SOF field. Following the SOF field, 11-bit or 29-bit identifier is transmitted to the CAN frame. Based upon the identifier, only related receiving nodes are enabled for reception while the other nodes go inactive unless exceptional event such as error occurs.
Two or more nodes may start the transmission simultaneously. In this case, the CAN standard provides multiple access arbitration scheme on the CAN bus. In the CAN standard, a carrier sense multiple access with bitwise arbitration (CSMA/BA) method is used for multiple access. Each of the nodes transmits the identifier after the SOF transmission, and drives the CAN bus with a logic level 0 or 1 according to a value of the identifier. The logic level 0 is referred to as dominant, and the logic level 1 is referred to as recessive. For example, it is assumed that the first node drives the identifier bit with dominant, and the second node drives the identifier bit with recessive. Thus, when two nodes drive the identifier bit with dominant and recessive at the same time, the state of the bus becomes a dominant state. The second node detects that the transmitted bit and the bit received from the bus are different indicting that its message has lower priority and subsequently stops the driving of the bus. As a result, it may be seen that a message having a small value of the identifier (ID) has a higher priority.
The node which obtains right to use the bus through the identifier competition may transmit a maximum of 64 bits during the data field. In order to determine a sampling time during the bit interval, the receiver detects bit transition from the logic level 0 to 1 or from the logic level 1 to 0. In order to ensure that the transition always occurs in a predetermined interval, when the same five or more bits are transmitted, a bit transition of different value is inserted after 5 consecutive same bit transmission. For example, when five bits of “1” are transmitted consecutively, a single bit transmission of “0” is transmitted on the CAN bus after 5 bit transmission and is removed in the receiver. The receiver detects the edge using a change of the bit transmission, and performs the bit detection by sampling after a predetermined offset time. The offset should be set to an appropriate value according to a delay of the system and the like.
Recently, demand for high-speed data transmission, specifically in vehicles including multimedia devices and the like, is increasing. Introduction of an additional high-speed standard transmission method other than the existing CAN interface may be considered. However, new scheme requires additional cable installation increasing vehicle weight and manufacturing costs. Therefore, recently, methods of increasing the data transmission rate based on the CAN standard have been proposed.
First, in order to improve the data transmission efficiency while maintaining the transmission rate of 1 Mbps in the CAN communication system, an efficient scheduling method through a channel delay analysis has been proposed. Additionally, methods for transmitting data at high speeds by overclocking have been proposed. In these methods, the data rate is increased during the overclocking period. However, the period for high data transmission is decreased compared to other standard CAN transmission period. Hence, the overall transmission rate is not increased significantly. In order to perform the high-speed transmission by increasing the data transmission interval by overclocking, a technique related to a CAN with flexible data-rate (CAN-FD) has been proposed. This is a technique in which the overclocking is performed with a maximum of 16 MHz in the data field after acquiring the bus right through the SOF and identifier transmission. After the data field transmission is completed, the rate is returned to an existing CAN rate of 1 Mbps. When CAN-FD devices operate along with the existing CAN devices, existing CAN receivers detect multiple edges in one-bit interval of 1 μs in CAN standard and report errors. Since the compatibility with the existing CAN receivers is not maintained, the CAN-FD scheme should be used between the nodes that support the CAN-FD method.
A method for maintaining the compatibility with the existing CAN receiver during high-speed transmission by overclocking like the CAN-FD method has been proposed. In this method, a high-speed clock is not transmitted over the entire bit interval of 1 μs. Instead, the clock is increased only in a gray zone where the existing CAN nodes do not perform the edge detection in order to maintain compatibility. However, since the data is not transmitted at high speeds over the entire bit interval, the rate is lower than that in the CAN-FD scheme.
All the above-proposed methods increase the rate by overclocking. However, since there is a limit to increasing the clock in the transmission method through the edge detection and the sampling according to the CAN standard and a response of a high-frequency band is limited due to a general frequency characteristic of a channel, it is difficult to ensure reliable reception when using the high-speed clock. In order for the receiver to perform the edge detection and the sampling, the receiver should receive a waveform as close to a rectangular one as possible. When using the high-speed clock, it is difficult for the receiver to completely receive the rectangular waveform, and thus the edge detection and bit detection performance is degraded. Therefore, a maximum rate of the CAN-FD that is being proposed currently is about 16 Mbps.
The present invention is a method in which a passband modulation signal for high-speed data transmission is transmitted in addition to the existing CAN signal that is transmitted in the same way as the CAN standard, and the compatibility with the existing CAN is maintained while enabling high-speed data transmission.
According to the increase of the bandwidth requirement for a vehicle and a controller, multimedia applications that cannot be supported by the existing CAN communication system are on the rise. The installation of a high-speed network in order to address this problem is very expensive. Specifically in the case of a vehicle, the increase in the weight and cost of the vehicle due to installation of additional cables can be prohibitive.
As vehicles become more sophisticated, electronic control apparatuses and multimedia apparatuses increase, and a huge amount of cabling is required to connect these separate apparatuses with each other. The cables take a significant part of the overall vehicle weight and manufacturing costs, posing issues in the reliability and component quality management. Hence, fundamental countermeasures are necessary to meet the challenges.
FIG. 2 illustrates a CAN communication system used in a conventional vehicle and the like. Each node on the CAN communication system includes a CAN controller, and the CAN controller may perform transmitting and receiving of a standard CAN bit stream, and serves to generate a standard CAN frame, process an identifier, transmit data, and perform error processing, and the CAN transceiver serves to load actual bits with dominant and recessive bits onto a CAN bus. In general, a differential signal is used for robustness to errors. When the recessive bit is transmitted, in general, the corresponding node does not drive the bus, and thus a state of the bus is set to return to a default value. When another node drives the bus in this state, the state of the bus changes to the one that the driving node specifies.
FIG. 3 illustrates a bus driving signal of the CAN transceiver illustrated in FIG. 2. The dominant signal corresponds to a bit 0, and the recessive signal corresponds to a bit 1. When the dominant signal is transmitted, the corresponding node transmits the signal to the bus, and when the recessive signal is transmitted, the corresponding node does not load the signal onto the bus. When the CAN nodes simultaneously drive the dominant and the recessive in the same bit interval, the state of the CAN bus becomes a dominant state. During the arbitration period, the node that transmits the dominant bit acquires the right to transmit the data on the bus, and the node that transmits the recessive bit waits until the bus is available later.